1. Field of the Invention
The present invention concerns furniture and accessories for use with computer data entry devices, particularly keyboards, in order that repetitive motion injuries to typists, and particularly carpal tunnel syndrome, may be avoided.
2. Description of the Prior Art
Discussion within the present section is drawn in substantial part from the Dec. 1, 1991, study report "An experimental test of a design prototype of the Protex.TM. system" by Alan Hedge and James R. Powers of the Human Factors Research Laboratory, Department of Design and Environmental Analysis, Cornell University, Ithaca, N.Y. 14853.
An anticipated increase in white-collar productivity through widespread computerization has failed to materialize. Part of the reason for this may be because when (i) computer monitors are viewed for long periods of time, and/or (ii) computer entry devices --primarily keyboards and mice--are used incorrectly, then these devices can become a source of physical stress and even injury. Stress diminishes productivity. Employee aversion to computers, even if subconscious, ultimately diminishes the effectiveness of the computers in the work place, and erodes business profitability through losses in employee productivity. Computer-induced injuries can result in absenteeism, and increases in health care costs.
As an example of a computer work place problem (although not the particular problem dealt with by the present invention), the notorious "QWERTY" keyboard layout was originally developed to intentionally reduce typing speed in order to avoid mechanical jamming of a manual typewriter. The "QWERTY" keyboard layout is grossly inefficient for data entry.
Perhaps equally as importantly, typewriter keyboards were originally positively sloped for reasons of mechanical design, and in order to accommodate the mechanical linkages between the rows of keys and the keybars. Computer keyboards continue this tradition, and are usually positively sloped if only so as to permit inexperienced users to see letters and key positions. By comparison, few other activities involving the hands and fingers--such as engraving, or the soldering of components on printed circuit boards--are regularly conducted on an inclined surface. Accordingly, several vestiges of typewriter design persist in the modern computer keyboard.
The two features of (i) keyboard layout and (ii) keyboard spatial attitudinal position that were once essential for the design of the mechanical typewriter now appear to play a significant negative role in the growing epidemic of musculo-skeletal problems among computer keyboard users. Foremost among these musculo-skeletal problems is carpal tunnel syndrome.
Carpal tunnel syndrome (CTS) is a cumulative trauma disorder (CTD) of the hand and wrist. It is believed to be caused primarily by the way in which work using the hands and wrists, including typing, is performed. In other words, it is an induced injury. A cumulative trauma disorder results from accumulated minor injuries to the musculo-skeletal system caused by the physical stresses of performing work over a prolonged period. Eventually the affected worker experiences pain, restricted mobility of the affected joint(s) and limbs, and soft tissue swelling. Reference Putz-Anderson, V. (1988) Cumulative Trauma Disorders: A manual for musculo-skeletal disorders of the upper limbs, (New York: Taylor & Francis).
According to the U.S. Bureau of Labor Statistics, compensable CTD cases increased from 20,000 in 1981 to 146,900 in 1989, and now account for 52% of all compensable work place injuries. Of these CTD cases, 125,000 were cases of compensable CTS. The incidence of CTS is increasing at an alarming rate, particularly among computer users. Although CTS can be treated with surgery, studies from Australia show that over half of the affected workers will suffer repeat occurrences of CTS within 1-2 years of returning to their job if nothing else is changed. Understanding the causes of CTS and redesigning the job to minimize or eliminate these causes is the best means of preventing and resolving CTS problems.
All finger movements involve the use of tendons. Tendons connect muscle to bone. When a muscle contracts the force is transferred to the appropriate bone via the tendons, which causes the bone to move (like pulling on the strings of a puppet). Each tendon in the hand and wrist is surrounded by a sheath (a tendon sheath) which secretes a lubricating fluid (synovial fluid) to minimize frictional forces as the fingers are flexed and extended (the tendon slides inside the tendon sheath). Movements of the fingers result from movements of tendons attached to the muscles of the forearm. When muscles in the upper forearm contract, the tendons that open (extend) the fingers contract, and as contraction continues the hand is pulled backwards (extension). When the muscles in the lower forearm contract the tendons that close (flex) the fingers contract, and if this continues the whole hand bends downwards (flexion). Tendon movement from full flexion to full extension can be as much as five centimeters (5 cm).
CTS is caused by cumulative damage to the finger tendons as they pass through a two to three centimeter (2-3 cm) long, narrow, rigid channel in the wrist--the carpal tunnel. With the hand oriented palm down, the roof of the carpal tunnel is formed by the arch of the carpal bones and the floor by the tough transverse carpal ligament. The carpal tunnel contains the tendons for the fingers, the radial artery, and the median nerve which transmits sensation for the thumb and the first 2.5 fingers. Sensation for the remaining 1.5 digits is transmitted via the ulnar nerve which runs outside of the carpal tunnel.
As the hand deviates from normal either (i) horizontally either towards the thumb (radial deviation) or towards the little finger (ulnar deviation), or (ii) vertically up or down, the pressure on the carpal tunnel increases. Vertical deviations (extension/flexion) create significant increases in carpal tunnel pressure. Reference Armstrong, T., Castelli, W. A., Evans, F. G. & Perez, R. D. (1984) Some histological changes in carpal tunnel contents and their biomechanical implications, Journal of Occupational Medicine, 26 (3), 197-201.
Accelerations from extension to flexion are thought to pose the greatest risk for CTS. Reference Marras, W. S. & Schoenmarklin, R. W. (1991) Wrist motions and CTD risk in industrial and service environments, in Y. Queinnic & F. Daniellou et. al., (eds.) Designing for Everyone: Proceedings of the Eleventh Congress of the International Ergonomics Association, Vol. 1, New York, Taylor & Francis, pp. 36-38.
When the hand is in a wrist neutral position (i.e., no vertical or horizontal deviation) then there is minimum pressure on the tendons and the median nerve in the carpal tunnel.
With occupational overuse of the fingers, minor trauma to the tendons and the sheaths may accumulate and eventually produce CTS. Repetitive movements with the hands in a deviated posture accelerate the onset of CTS. Reference Chaffin, D. B. & Anderson, G. (1984) Occupational Biomechanics, (New York: John Wiley & Sons).
As the tendons or their sheaths become irritated and inflamed, the resulting swelling increases the pressure on the median nerve, which initially causes tingling, then numbness, and eventually disabling pain when the fingers are moved. Computer users are particularly at risk because of the large number of finger movements which the fingers may make in a short time. For example, a data entry worker who averages 13,000 key strokes per hour will make over half-a-million finger movements per week. In short, the three major risk factors for CTS are poor posture, pressure in the carpal tunnel, and lack of pauses to allow time for tissue repair.
The use of QWERTY keyboard layout, which can cause some ulnar deviation of both hands, and a positive keyboard angle which places the hands in an extended posture, combine to increase the risks of CTS. Over time these factors accelerate the accumulation of trauma to the hands/wrists, and this cumulative trauma is now appearing as the epidemic of CTS cases. Also, QWERTY keyboards usually are asymmetrical (i.e., the numeric keyboard is to the right of the QWERTY keys) and users tend to center the keyboard on their screen rather than centering QWERTY on the screen. This can result in users sitting in,twisted postures which increase the risks of back, shoulder and neck problems.
Accordingly, and in recapitulation, the major contributing factors to the occurrence of CTS are believed to fall primarily within the categories of (i) poor posture, (ii) no or insufficient pauses during work, and (iii) undesirable pressures. "Poor posture" includes (i) wrist extension, (ii) hand deviation, and (iii) poor seated posture. "No or insufficient pauses" include (i) repetitive movements, (ii) no or inadequate micro-breaks, and (iii) impaired tissue repair. "Undesirable pressures" include those pressures resultant from (i) flexion/extension accelerations, (ii) increased carpal tunnel pressure, and (iii) increased tissue trauma.
Because of the significance of the CTS problem, a number of previous products have attempted to reduce CTS risks.
First, the layout of data entry keyboards have been modified. Keyboard re-designs to minimize horizontal radial or ulnar deviation have been developed. Reference Grandjean, E. (1988), The Ergonomics of Computerized Offices, (New York: Taylor & Francis); also Grandjean, E. (1988), Fitting the Task to the Man, 4th ed. (New York: Taylor & Francis). However, the problem of vertical deviation (extension) remains even with these keyboards. Also, postural risks from using other input devices (e.g., mouse) are obviously unaffected by modification to keyboard layout.
Second, wrist rests have been provided. Each arm weighs about 2.5% of a human's total body weight. The ability to rest the wrists on a support helps to reduce muscular activity in the forearm and incidentally reduce pressure in the carpal tunnel. However, problems of flexion/extension and ulnar/radial deviation remain because of the design and slope of the keyboard. Reference Parsons, C. A. (1991) , "Use of wrist rest by data input VDU operators" appearing in Contemporary Ergonomics 1991--Proceedings of the Ergonomics Society's 1991 Annual Conference, (London, Taylor & Francis) pp. 319-321. Parsons tested nine different wrist rests on forty full time data input VDU operators. None of the operators found them useful, and 10% commented that discomfort increased when using a wrist rest with a traditional keyboard.
Third, full motion fore-arm supports have been provided. These products provide full motion fore-arm support for the worker. Each arm is rested in a mobile support which takes the arm weight for all horizontal movements. However, as with wrist rests, problems of flexion/extension and ulnar/radial deviation remain because of the design and angle of the keyboard, and in a short-term test the use of full motion fore-arm supports resulted in a slight slowing of typing speed. Reference Powers, J. R. (1991), "Effects of full-motion forearm supports on keyboard operator hand-wrist posture, keyboarding performance, and keyboarding accuracy", Master's Thesis, Dept. Design & Environmental Analysis, Cornell University.
One existing, extensive, composite, and sophisticated system for avoidance or alleviation of CTS is the Protex.TM. System available from Proformix, Inc. Whitehouse Station, New Jersey. (Protex.TM. is a trademark of Proformix, Inc.) Unlike keyboards which are angled on a positive incline, or keyboard trays which are horizontal surfaces that hold the keyboard at a positive angle to the body, the Protex.TM. System supports and presents the keyboard at an angle ranging from zero degrees (0.degree., or level) to various angular slopes downwards and away from the worker. The result of flattening the keyboard angle, or sloping the keyboard away from the worker, is that the fingers operate the keys with the hands permanently in a vertically wrist-neutral position. This re-orienting of the keyboard, combined with the use of a broad wrist-support to reduce muscular activity associated with unsupported forearms, is intended to significantly reduce the risk of RSI. Indeed, in Australian field tests of this type of design, Stack (1987, 1988) reports that slanting the keyboard away from the operator so as to flatten the angle of the wrists and fingers was a major factor in solving the problems of RSI in the Tasmanian public service. Reference Stack, B. (1987), Keyboard RSI: the practical solution, Meuden Press, Hobart. Reference also Stack, B. (1988) papers in press cited by Patkin, M. in "Neck and arm pain in office workers: causes and management", appearing in Sauter, S. L., Dainoff, M. J. & Smith, M. J. (eds.) Promoting health and productivity in the computerized office: models of successful ergonomic interventions, Chap. 13, (Taylor & Francis, New York), pp. 207-231, 1990.
Experiments at Cornell University with the Protex.TM. System have reportedly shown that a negative slope keyboard significantly reduces wrist extension and places the hand in a vertically wrist neutral position. Reference "An experimental test of a design prototype of the Protex.TM. system" by Alan Hedge and James R. Powers of the Human Factors Research Laboratory, Department of Design and Environmental Analysis, Cornell University, Ithaca, N.Y. 14853. This finding is in agreement with that of the Australian research. Reference Stack (1987, 1988), op cit. Subjects using the negatively sloped keyboard support sat 11 cm farther from the VDT screen, but the viewing distance remained within the preferred range of distances 61-93 cm. Reference Grandjean, E. (1988) Fitting the Task to the Man, 4th ed., (New York: Taylor & Francis).
The ulnar deviation of both hands was comparable in both conditions. Research showed that ulnar deviation varies between ten to twelve degrees (10.degree.-12.degree.) for the right hand even when subjects are working with a split keyboard with an opening angle of twenty-five degrees (25.degree.) and a ten degrees (10.degree.) sloping fore-arm support. Reference Grandjean, E. (1988), op cit. The ulnar deviation of thirteen degrees (13.degree.) for the right hand that was found in this study is comparable with results reported by Grandjean, and this suggests that even a redesigned split keyboard does not dramatically change ulnar deviation. Some ulnar deviation seems inevitable with keyboard use, and this is not thought to be a major CTS risk factor.
Several additional products are commercially available that can place a keyboard at a negative angle, such as the Details.TM. keyboard support (Details.TM. is a trademark of Steelcase, Inc.) and the Flex-Rest.TM. keyboard support (Flex-Rest.TM. is a trademark of Flex-Rest, Inc.). However, these products are more difficult to adjust, do not provide comparable wrist neutral support, do not support mouse work or pen-based work. Additionally, products are metal framed and they do not necessarily reduce risks from electromagnetic fields (EMF).
The present invention will be seen to accommodate the realities of existing office furniture, and the existing organization of keyboarding stations. A great deal of existing office furniture--which furniture normally presents a level surface for supporting a keyboard at or near the ergonomic standard height (for Americans, circa 1993) of twenty-eight and one-half inches (28.5")--cannot reasonably nor economically be discarded. Moreover, multitudinous existing computer keyboards make no accommodation to being oriented at a negative angle.
The present invention will be seen to be directed to doing the best that can reasonably be done towards ergonomically accommodating individuals of considerably different sizes (ranging from a 5th percentile female to a 95th percentile male) in their use of an existing computer keyboard placed upon an existing surface (which surface is typically not adjustable in height).
In so doing, and so accommodating, a first challenge to ergonomic design is the considerably different angles of approach to a keyboard surface resting upon an ergonomic standard twenty-eight and one-half inches (28.5") high desk made by the fingers and forearms of a 5th percentile female versus a 95th percentile male. When seated upon a standard chair, a 95th percentile male typically enjoys an ergonomically-correct straight wrist-hand angle in the placement of his fingers atop a keyboard surface that rests upon an ergonomic standard twenty-eight and one-half inches (28.5") high desk. However, when seated upon the same standard chair, a 5th percentile female's forearms will approach the keyboard from an extreme, twenty-five degree (25.degree.), down angle, and she must bend her wrists and fingers in considerable flexion. Most keyboard typists in the American work force circa 1993 are female. Curiously, and nonetheless, the American office furniture that is most commonly used by females is better ergonomically designed--at least in its support of computer keyboards--for use by males!
According to this first ergonomic challenge, it would be useful if some improvement--consistent with existing conditions of the office work place environment--could be made so as to permit a better angle of approach of the wrists and hands of variously sized or variously seated typists to a pre-existing computer keyboard.
Another ergonomic challenge is stress relief, and fatigue avoidance. Again, any realistic solution is likely to be constrained by the existing conditions of the office work place environment. However, it would be useful if an ergonomic device could make some flexible, and realistic, accommodation to relieving strain on a typist's forearms, wrists and/or hands by improving support of the typist's wrists. Reference Parsons (1991) and Powers (1991), op cit.